The invention is directed to a separator apparatus for separating solids from a gas-solid containing feed resulting in a gas-rich stream, the separator comprising:
an upright hollow circular housing fluidly connected to a dipleg for discharging solids positioned below the housing;
a gas outlet tube for discharging the gas-rich stream from the circular housing, which outlet tube protrudes substantially co-axial from the top of the housing;
inlet means for the gas-solids feed so arranged to create, in use, a vortex flow in the circular housing.
Such an apparatus is described in U.S. Pat. No. 5,391,289. This patent publication describes a cyclone separator which is used as a secondary separation step to separate solid catalyst particles from the reactor effluent of a fluid catalytic cracking (FCC) reactor. In a FCC process hydrocarbons are cracked at high temperature in the presence of a solid catalyst to more desired components, for example gasoline and lower olefins. In the field of FCC these cyclone separators are also referred to as secondary cyclones. Other publications describing these secondary cyclones in a FCC process are for example U.S. Pat. Nos. 5,055,177, 5,376,339, EP-A-299650, EP-A-488549 and EP-A-309244.
A disadvantage of these secondary cyclones is that coke deposit may form on the walls of these apparatuses. Coke forming is a result of the hydrocarbons present in the feed to the cyclone and the relatively high temperatures of the gasses fed to the cyclones. Large pieces of coke can fall from the wail into the dipleg and cause to clog the dipleg. When a dipleg is clogged the cyclone will not function in an optimal manner as a solid-gas separator and the fluid catalytic cracking process will have to be shut down in order to remove the coke from the dipleg. Because FCC processes are expected to run many months and even years between planned shutdowns any unexpected shutdown will cause considerable economic damage.
The object of this invention is to avoid the problems associated with clogging of the diplegs of the separator apparatus.
The object is achieved by the following apparatus. A separator apparatus for separating solids from a gas-solid containing feed resulting in a gas-rich stream, the separator comprising:
an upright hollow circular housing fluidly connected to a dipleg for discharging solids positioned below the housing; a gas outlet tube for discharging the gas-rich stream from the circular housing, which outlet tube protrudes substantially co-axial from the top of the housing, inlet means for the gas-solids feed so arranged to create, in use, a vortex flow in the circular housing; and a sieve positioned between the lower part of the circular housing and the upper part of the dipleg, which sieve has openings which do not allow particles having a diameter greater than 0.75 times the diameter of the dipleg to pass the sieve and enter the dipleg and wherein the total area of the openings in the sieve is greater than 2 times the cross sectional area of the dipleg.
It has been found that when such a sieve is used less problems due to clogging of the dipleg occur. Because of the sieve a reduction of the normal swirl movement in the dipleg is observed. As a result the pressure difference per length of dipleg will increase making it possible to use a shorter dipleg. This is very advantageous, especially when these cyclones are present within a vessel, for example a stripping vessel of a FCC process. The length of a dipleg is often the determining factor for the dimensions of the vessel. Thus shorter diplegs result in that smaller vessels can be employed.